In late 1938, the Bf 109E entered production. To improve on the performance afforded by the 441–515 kW (600–700 PS) Jumo 210, the larger, longer Daimler-Benz DB 601A engine was used, yielding an extra 223 kW (300 PS) at the cost of an additional 181 kg (400 lb). A much bigger cooling area was needed to disperse the extra heat generated by the DB 601 and this led to the first major redesign of the basic airframe. Enlarging the existing nose mounted radiator sufficiently to cool the engine would have created extra weight and drag, negating some of the performance gains afforded by the increased power, so it was decided to move the main radiators to the wings, leaving the oil cooler under the nose in a small, streamlined duct. The new radiator position also had the effect of counterbalancing the extra weight and length of the DB 601, which drove a heavier three-bladed VDM propeller. To incorporate the new radiators the wings were almost completely redesigned and reinforced, with several inboard ribs behind the spar being cut down to make room for the radiator ducting. Because the radiators were now mounted near the trailing edge of the wing, coinciding with the increased speed of the airflow accelerating around the wing's camber, the overall cooling installation was more efficient than that of the Jumo engined 109s, albeit at the cost of extra ducting and piping, which could be vulnerable to battle damage. In addition the lowered undercarriage could throw up mud and debris on wet airfields, potentially clogging the radiators.

To test the new 1,100 PS (1,085 hp, 809 kW) DB601A engine, two more prototypes (V14 and V15) were built, each differing in their armament. While the V14 was armed with two 7.92 mm (.312 in) MG 17s above the engine and one 20 mm MG FF in each wing, the V15 was fitted with the two MG 17s mounted above the engine only. After test fights the V14 was considered more promising and a pre-production batch of 10 E-0 was ordered. Batches of both E-1 and E-3 variants were shipped to Spain for evaluation, and first saw combat during the final phases of the Spanish Civil War.

Bf 109E-3E-1[edit]The production version E-1 kept two 7.92 mm (.312 in) MG 17s above the engine and two more in the wings. Later, many were modified to the E-3 armament standard. The E-1B was a small batch of E-1s becoming the first operational Bf 109 fighter bomber, or Jagdbomber (usually abbreviated to Jabo). These were fitted with either an ETC 500 bomb rack, carrying one 250 kg (550 lb) bomb, or four 50 kg (110 lb) bombs. The E-1 was also fitted with the Reflexvisier "Revi" gunsight. Communications equipment was the FuG 7 Funkgerät 7 (radio set) short-range radio apparatus, effective to ranges of 48–56 km (30–35 mi). A total of 1,183 E-1 were built, 110 of them were E-1/B.[11][12]

E-2[edit]Only very limited numbers of the E-2 variant were built, for which the V20 prototype served as basis. It was armed with two wing mounted, and one engine mounted Motorkanone MG FF cannon, which gave considerable trouble in service, as well as two synchronized MG 17s cowl machine guns. In August 1940, II./JG 27 was operating this type.[16][17]

E-3[edit]To improve the performance of the Bf 109E, the last two real prototypes, V16 and V17 were constructed. These received some structural improvements and more powerful armament. Both were the basis of the Bf 109 E-3 version. The E-3 was armed with the two MG 17s above the engine and one MG FF cannon in each wing.[18][19] A total of 1,276 E-3 were built, including 83 E-3a export versions.[11][12]

Bf 109E-4E-4[edit]The E-3 was replaced by the E-4 (with many airframes being upgraded to E-4 standards starting at the beginning of the Battle of Britain) which was different in some small details, most notably by using the modified 20 mm MG-FF/M wing cannon and having improved head armour for the pilot. With the MG FF/M it was possible to fire a new and improved type of explosive shell, called Minengeschoß (or 'mine-shell') which was made using drawn steel (the same way brass cartridges are made) instead of being cast as was the usual practice. This resulted in a shell with a thin but strong wall, which had a larger cavity in which to pack a much larger explosive charge than was otherwise possible. The new shell required modifications to the MG FF's mechanism due to the different recoil characteristics, hence the MG FF/M designation.

The cockpit canopy was also revised to an easier-to-produce, "squared-off" design, which also helped improve the pilot's field of view. This canopy, which was also retrofitted to many E-1s and E-3s, was largely unchanged until the introduction of a welded, heavy-framed canopy on the G series in the autumn of 1942. The E-4 would be the basis for all further Bf 109E developments. Some E-4 and later models received a further improved 1,175 PS (1,159 hp, 864 kW) DB601N high-altitude engine; known as the E-4/N; owing to priority being given to equipping Bf 110s with this engine, one fighter gruppe was converted to this version, starting in July 1940.[20] The E-4 was also available as a fighter-bomber with equipment very similar to the previous E-1/B. It was known as E-4/B (DB 601Aa engine) and E-4/BN (DB 601N engine). A total of 561 of all E-4 versions were built,[12] including 496 E-4s built as such: 250 E-4, 211 E-4/B, 15 E-4/N and 20 E-4/BN.[11]

E-5, E-6[edit]The E-5 and E-6 were both reconnaissance variants with a camera installation behind the cockpit. The E-5 was a reconnaissance variant of the E-3, the E-6 was a reconnaissance variant of the E-4/N. Twenty-nine E-5s were built and nine E-6 were ordered.[11]

E-7[edit]The E-7 was the next major production variant, entering service and seeing combat at the end of August 1940.[21] One of the limitations of the earlier Bf 109E was their short range of 660 km (410 mi) and limited endurance, as the design was originally conceived as a short-range interceptor. The E-7 rectified this problem as it was the first subtype to be able to carry adrop tank, usually a 300 L (80 US gal) capacity unit mounted on a rack under the fuselage, which increased their range to 1,325 km (820 mi). Alternatively, a bomb could be fitted and the E-7 could be used as a Jabo fighter-bomber. Previous Emil subtypes were progressively retrofitted with the necessary fittings for carrying a drop tank from October 1940.[22] Early E-7s were fitted with the 1,100 PS DB 601A or 1,175 PS DB 601Aa engine, while late-production ones received 1,175 PS DB 601N engines with improved altitude performance – the latter was designated as E-7/N.[23] A total of 438 E-7s of all variants were built.[24]